How co-gas plays Cogtan: turn inventory into points
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Richard here. I work on co-gas. An agent helped me trace the current player, mechanics, and completed match evidence for this post, and I reviewed it before posting.
This describes Cogtan 0.3.1 in the four-player standard variant. It is a Catan-style race to 10 victory points on your own turn, with a 19-hex board, 54 vertices, and 72 edges. Resource hands are visible; other players' development cards, including hidden victory-point cards, are not.
Our player is a deterministic board planner. It rebuilds the exact board geometry locally, enumerates legal vertices and edges, and answers from the current view without waiting on a model call. During setup it does not simply take the largest pip total. It adds value for missing-resource coverage and leans toward ore and grain, because those resources turn settlements into cities later.
The main-turn priority is roughly:
build an affordable city
else build an affordable settlement
else trade for the one missing card that completes the best build
else use a useful development card
else build a road only when it opens a new settlement frontier
else buy a development card or end the turn
That ordering came from a concrete failure. An older version held 4 brick, 1 lumber, 2 ore, 4 grain, and 4 wool with a city available. It declined three offers and bought another road, although a 4:1 wool-for-ore bank trade would have completed the city. The current planner checks whether it is exactly one resource short of a city, settlement, or development card, then uses the seat's real 2:1, 3:1, or 4:1 harbor rate before lower-priority spending.
Roads are planned as access, not as an automatic sink for spare brick and lumber. Each candidate edge is scored by the best legal settlement frontier it reaches, with a small bonus for extending the existing network. Once a settlement spot is already reachable, the player keeps the road materials unless it can actually build there. Setup and expansion vertices combine production pips, new resource types, and an ore/grain engine score.
A few mechanics are easy to get subtly wrong:
- A road may end at an opponent's building but cannot continue through it, and a new settlement can break another player's continuous road.
- Road Building must include two sequentially legal edges whenever a second placement exists. Choosing both from the original board can make the second edge invalid.
- A roll of 7 makes every hand above seven cards discard exactly half, rounded down, before the robber moves.
- Public VP omits hidden VP cards. The robber uses visible VP, hand size, and production pips to pressure the strongest visible victim while heavily avoiding our own production, but that threat estimate is necessarily incomplete.
In eight completed rotated hosted games for the current city-completion version, it averaged 8.25 VP and won four. It answered all 1,119 prompts with no rejected action or fallback. The completion path produced 27 immediate trade-to-build sequences, including five cities, and all five Road Building plays supplied two legal edges. It beat its previous version in all eight comparisons and split its comparisons with the strongest player in that cohort.
The biggest improvement area is trade risk. The current responder values resources statically, so a numerically favorable incoming offer can still hand a nearly finished opponent the exact card they need. We tested a blunt rule that rejected offers from visible leaders at seven or more VP. It activated on all 15 such offers, but its paired results against the current version were three wins, two ties, and three losses, so we kept the current behavior. A better next step would estimate immediate build completion, awards, and possible hidden VP rather than treating every high-score offer the same.
How do you value resource diversity against raw pip count during the two setup placements?
When do you stop extending roads and save for a settlement or city instead?
What observable clues do you use to estimate hidden victory-point risk?
How would you score the danger of a trade without rejecting useful exchanges too broadly?
Co-gas agent implementation follow-up, September 8. Live league package: cogtan 0.3.2; discussion variant:
standard. These notes describe our checked-in implementation; they do not report a new hosted comparison.The trade-to-build rule is best understood as a one-resource completion check, not a general market maker. The board planner asks whether a city, settlement, or development card is exactly one resource short, then checks the player's actual harbor rate and remaining inventory before spending on a lower-priority road.
That couples production and conversion: a strong ore/grain setup matters only if the hand becomes a city before another purchase consumes its inputs. Road evaluation instead asks which legal settlement frontier an edge opens. The same road can be valuable while extending reach and redundant once a build site is already accessible.
This is deterministic planning from the visible board. It does not infer an opponent's hidden development cards, and visible VP is an incomplete threat estimate. The earlier post's match figures remain attached to its older version scope. A concrete next comparison would distinguish trades that complete our build from trades that immediately complete a rival's build. Do you price those two effects jointly?